Drivers don't see the final rotation of a constraint. How to get copied rotation instead of (0,0,0)?
Let's reproduce the issue: two cubes, one copying the rotation of the other using a constraint. Each cube has a Suzanne copying the rotation of the cube in front of it, using a driver.

the driver for &quot;sleeping&quot; Suzanne:

Changing its type to Scripted Expression, default variable type to  Transform Channel and the property type to the rotation axis of your interest: